In recent years, technology on semiconductor devices having thin film transistors (hereinafter referred to as TFTs) has been developed extensively. The manufacturing of a semiconductor device can be broadly classified into anterior steps and posterior steps. One of the posterior steps is a step of cutting semiconductor elements provided with integrated circuits and packaging each of the cut semiconductor elements. In the packaging step, a cover is attached to the cut semiconductor element to protect the semiconductor element from foreign particles. The packaged semiconductor device is called a semiconductor package. Since the semiconductor package can achieve size reduction and capacity increase for circuit mechanisms and appliances, the semiconductor package is widely used for various kinds of electronic appliances. Moreover, by the use of the semiconductor package, assembly and manufacturing process can be simplified and a semiconductor device can be reduced in size.
As a method for forming an electrode that connects a semiconductor device and an external terminal to each other, an electroplating method, a stud bump method, a printing method, or an evaporation method is given. In the stud bump method, an electrode with a sharp apex is formed in such a way that a ball is formed at an edge of a metal wire by thermal energy, the formed ball is bonded with an integrated circuit by capillary while applying pressure thereto, and then the metal wire is cut. When the electrode formed in this manner is inserted in an antenna, the electrode of the semiconductor device can have physical contact with the external terminal. In addition, since the electrode can be formed to have a sharp apex, the stud bump method is known as a method by which favorable electric contact is also possible and which provides high reliability. The stud bump method can be applied to products provided with devices having circuits mounted, such as various integrated circuits to be provided over a mother board (also called a main board) for a computer. Moreover, the stud bump method can also be used to connect an antenna and an integrated circuit of a semiconductor device capable of wireless communication, such as an RFID (Radio Frequency Identification) tag.
When the electrode formed in the semiconductor device, which is to be connected to an external circuit, has a projection portion in its center, the connection between the integrated circuit and the external circuit becomes favorable. This is because, by having a projection portion in the center of the electrode, the connection becomes possible through a connection point of the projection portion (for example, Reference 1: Japanese Published Patent Application No. 2001-175829).
Alternatively, the electrode can be formed by a screen printing method. As an example of a technique for forming an electrode by a screen printing method, for instance, Reference 2 (Japanese Published Patent Application No. 2005-340282) is given.